The intestinal mucosa maintains its integrity through spatiotemporal regulation of proliferation, differentiation, migration, and cell death along the crypt-luminal axis of the intestine. The molecular mechanisms that coordinate these events, particularly in the context of injury repair, are not well understood. Furthermore, it is not known how perturbations of these processes impact cell junction formation and barrier function. Kruppel- like factor 5 (KLF5) is a member of a family of transcription factors that function in the regulation of diverse cellular processes including development, proliferation, and differentiation. KLF5 is highly expressed in the proliferative component of the intestinal epithelium, and has been shown to promote proliferation of intestinal epithelial cells in vitro and in vivo. Recent dat from mice with intestine-specific deletion of Klf5 indicate that KLF5 is required for maintenance of intestinal crypt architecture and epithelial barrier integrity. In addition, it was shown recenty that KLF5 is necessary for mucosal healing in the dextran sulfate sodium (DSS) mouse model of colitis. Based on these results, we hypothesize that KLF5 controls renewal and maturation of epithelial cells along the crypt-luminal axis and is required for intestinal epithelial integrity. he following aims have been developed to test this hypothesis: (I) Define the role of KLF5 in regulating proliferation, migration, and maturation of epithelial cells along the crypt-luminal axi of the intestine. Genetic mouse models and cell culture systems will be used for ectopic expression or inhibition of KLF5 to explore the role of KLF5 in regulating processes involved in intestinal epithelial homeostasis. (II) Determine the requirement of KLF5 in maintaining intestinal epithelial barrier function. The effects of KLF5 expression on intestinal permeability and the formation of apical junctional complexes will be determined. (III) Examine the role of KLF5 in intestinal epithelial wound repair. These experiments will test whether increased levels of KLF5 can improve outcome and epithelial healing in DSS-induced colitis. Several methods to increase KLF5 expression in the mouse colon will be tested, including adenoviral delivery, nanoparticle delivery and transgenic expression. Reciprocal studies using mice with inducible intestine-specific deletion of Klf5 will also be conducted to test whether KLF5 is necessary for repair of intestinal injury. The long-term goal of these studies is to elucidate the molecular mechanisms that regulate intestinal epithelial integrity, both in situations of tissue renewal and injury repar. The proposed studies will contribute to a better understanding of factors that coordinate the processes of proliferation, migration, and differentiation to maintain intestinal architecture and barrier function. In particular, these studies will explore novel roles for KLF5 in the processes o epithelial maturation, migration, and cell junction formation, and the possibility for KLF5 as a therapeutic target in disease conditions such as inflammatory bowel disease. PUBLIC HEALTH RELEVANCE: One of the major complications and possibly causes of inflammatory bowel disease (IBD) is disruption of the barrier function of the intestinal epithelium which exacerbates and prolongs active flare-ups. Understanding how the injured mucosa is repaired and identifying key molecules involved in the maintenance and repair of the epithelial barrier function can provide potential therapeutic targets directed at mucosal healing in IBD patients.